feat: Custom domains route53 support

[praneetap]

Issue #, if available:
#1128 #1129, #783
Description of changes:
Adding Route53 resource generation for custom domains feature.
Description of how you validated changes:
unit tests only so far.
Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1165 into develop will decrease coverage by 0.14%.
The diff coverage is 85.71%.

@@             Coverage Diff             @@
##           develop    #1165      +/-   ##
===========================================
- Coverage    94.47%   94.33%   -0.15%     
===========================================
  Files           71       72       +1     
  Lines         3677     3724      +47     
  Branches       726      733       +7     
===========================================
+ Hits          3474     3513      +39     
- Misses         103      107       +4     
- Partials       100      104       +4

Impacted Files	Coverage Δ
samtranslator/model/route53.py	100% <100%> (ø)
samtranslator/model/sam_resources.py	95.59% <100%> (+0.02%)	⬆️
samtranslator/model/api/api_generator.py	94.66% <82.97%> (-1.86%)	⬇️

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